1. Technical Field of the Invention
The present invention relates to a device substrate and a method for producing the device substrate.
2. Description of the Related Art
Group III–V semiconductor materials such as GaN and group II–VI semiconductor materials such as ZnO have been developed as materials for constructing luminous elements such as a laser diode, since these materials are direct transition semiconductor materials having an energy gap of 2 to 6 eV.
Since a good quality and large single crystal substrate constituting these materials currently cannot be obtained for forming (depositing) a thin layer of these semiconductor materials today, these materials are inevitably deposited by hetero-epitaxial growth on a substrate having a different lattice constant and thermal expansion coefficient.
For example, there has been the following problems for forming AlN crystals or a GaN crystals on a Si(111) substrate by hetero-epitaxial growth.
While the Si—Si distance of the Si(111) face is 0.384 nm, the lattice constants of GaN are a=0.3192 nm and c=0.5196 nm, and the lattice constants of AlN are a=0.3112 and c=0.4980. Therefore, the lattice mismatch of these crystals with the Si(111) face is as large as 50% or more.
Consequently, when these semiconductor materials are grown on the Si(111) substrate by hetero-epitaxial growth, the crystals of these materials suffer from lattice distortion causing a decrease in quality. The characteristics of a luminous element formed using these semiconductor materials are also inevitably deteriorated.
In view of the foregoing, one object of the present invention is to provide a device substrate comprising high quality semiconductor material layers, and a method for producing such device substrate.